package com.rd.student.wulian.wanggaobo.day0728.practice01;

import java.util.Scanner;

public class Triangle {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int layer = sc.nextInt();
        int sum = 0;
        for (int i = 1; i <= layer; i++) {

            sum = sum+i;
        }
        System.out.println(sum);
    }
}
